This section provides background information related to the present disclosure which is not necessarily prior art.
FIG. 1 shows an example of a typical prior art single module UPS system, referred to herein as UPS module 100. The basic elements of UPS module 100 are rectifier 102, inverter 104, output transformer 106, a backup DC power source 108, and a controller 110. UPS module 100 also includes a bypass switch (not shown). An input of rectifier 102 is coupled to a source of AC power (not shown). An output of rectifier 102 is coupled to a DC bus 112. An input of inverter 104 is coupled to DC bus 112. An output 105 of inverter 104 is coupled to a primary side 114 of output transformer 106. A secondary side 116 of output transformer 106 is coupled to output 118 of UPS module 100. A Grass filter circuit 120 is coupled to the secondary side 116 of output transformer 106. A filter circuit 122 is coupled to the primary side 114 of output transformer 106.
Controller 110 controls UPS module 100 including controlling inverter 104 by varying the duty cycle of the switching devices in inverter 104 so that inverter 104 provides a desired output voltage. In this regard, controller 110 has inputs 124 and outputs 126. Inputs 124 include inputs coupled to current transformers CT that sense currents in various parts of UPS module 100 such as shown in FIG. 1, including a load current flowing through output 118 of UPS module 100, and voltage sensors VS that sense voltage such as a primary side voltage at primary side 114 of output transformer 106 or a secondary side voltage at secondary side 116 of output transformer 106.
A multi-module UPS system includes two or more single module UPS systems such as UPS module 100 coupled in parallel. FIG. 2 shows an example of a multi-module UPS 200 having two UPS modules 100 coupled in parallel.